1. Introduction

Ongoing rapid advances in power electronics and communication technologies are facilitating the development of smart grids that are characterized by hosting distributed generation units (DGs). There are many benefits of smart grids such as enhancing power reliability and power quality, improving safety and cyber security, maximizing energy utilization and efficiency, environment protection and conservation, and increasing financial revenues [1]. For instance, as reported in [2], smart grids could reduce greenhouse gas emissions by up to 18%. The integration of renewable-based DGs alters distribution systems so that rather than having passive structures, with unidirectional power flow, they become active distribution networks (ADNs), with multidirectional power flow. Voltage regulation is considered one of the main operational challenges that accompany high penetration levels of renewable-based DGs. RES, such as wind and solar energy, can significantly change the voltage profile of smart grids and interact negatively with conventional schemes of controlling onload tap changers (OLTCs). Another factor is the growing penetration of PEVs, which creates additional stress on voltage control devices due to their stochastic and concentrated power profiles. These combined generation and load power profiles can lead to overvoltages, undervoltages, high system losses, excessive tap operation, infeasible solutions (hunting) with respect to OLTCs, and/ or limits on the integration of either PEVs or RES.
